What is a fetus? After the embryonic period has ended at the end of the 10th week of pregnancy, the embryo is now considered a fetus. A fetus is a developing baby beginning in the 11th week.

It begins at conception and ends at birth. Many changes occur to the fetus and the pregnant person in this time. In human prenatal development, fetal development begins from the ninth week after fertilization (which is the eleventh week of gestational age) and continues until the birth of a newborn.